Piezoelectric/electrostrictive porcelain composition and method of manufacturing the same

ABSTRACT

A piezoelectric/electrostrictive porcelain composition is provided, including at least Nb, Ta, and one or more alkali metal elements, wherein a molar ratio of the Nb, Ta, and alkali metal element is represented by a non-stoichiometric composition ratio.

BACKGROUND OF THE INVENTION

The present invention relates to a piezoelectric/electrostrictiveporcelain composition, and a method of manufacturing the composition,more particularly to a piezoelectric/electrostrictive porcelaincomposition capable of obtaining a piezoelectric/electrostrictive devicewhich is dense and which is superior in crystallinity and which exhibitssuperior piezoelectric/electrostrictive characteristics, a method ofmanufacturing the composition, and a piezoelectric/electrostrictivedevice having superior piezoelectric/electrostrictive characteristics.

BACKGROUND ART

Heretofore, a piezoelectric/electrostrictive device has been known as adevice capable of controlling micro displacement of the order ofsub-microns. Especially, a piezoelectric/electrostrictive device issuitable for the control of the micro displacement. In the device, apiezoelectric/electrostrictive article (a piezoelectric/electrostrictiveportion) constituted of a piezoelectric/electrostrictive porcelaincomposition and an electrode portion to which a voltage is applied arelayered on a substrate made of a ceramic. Additionally, the device hassuperior characteristics such as a high electromechanical conversionefficiency, a high-speed response, a high durability, and a saved powerconsumption. The piezoelectric/electrostrictive device is used invarious applications such as a piezoelectric pressure sensor, a probemoving mechanism of a scanning type tunnel microscope, a rectilinearguide mechanism in an ultra-precise working device, a servo valve forhydraulic control, a head of a VTR device, a pixel constituting a flatpanel type image display device, and a head of an ink jet printer.

Moreover, the piezoelectric/electrostrictive porcelain compositionconstituting the piezoelectric/electrostrictive article is alsovariously investigated. For example, there have been disclosed aPb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃—PbZrO₃ three-components dissolvedcomposition, and a piezoelectric/electrostrictive porcelain compositionin which a part of Pb in the composition is replaced with Sr, La or thelike (see, e.g., Patent Documents 1 and 2). As to thepiezoelectric/electrostrictive article itself which is the mostimportant portion that determines a piezoelectric/electrostrictivecharacteristic of the piezoelectric/electrostrictive device, there isexpected to be obtained the piezoelectric/electrostrictive device havinga superior piezoelectric/electrostrictive characteristic (e.g.,piezoelectric d constant).

However, the PZT-based composition unavoidably contains lead (Pb).Especially, in recent years, an influence on global environments, suchas elution of lead (Pb) due to acid rain, has tended to be regarded as aproblem. As a piezoelectric/electrostrictive material in which suchinfluence on the environments is considered, there is disclosed aBaTiO₃-based piezoelectric/electrostrictive porcelain compositioncapable of providing a piezoelectric article or a piezoelectric devicewhich exhibits the satisfactory piezoelectric/electrostrictivecharacteristic although lead (Pb) is not contained. However, there is aproblem that Curie point of the BaTiO₃-basedpiezoelectric/electrostrictive porcelain composition is as low as about120° C., and the composition is not suitable for use on high-temperatureconditions.

Moreover, there is developed an (LiNaK)(NbTa)O₃-basedpiezoelectric/electrostrictive porcelain composition as a non-leadpiezoelectric/electrostrictive material in which the influences on theenvironments are similarly considered. The composition has Curie pointwhich is higher than that of the BaTiO₃-basedpiezoelectric/electrostrictive porcelain composition (see, e.g., PatentDocument 3).

However, in many of general piezoelectric/electrostrictive porcelaincompositions including the (LiNaK)(NbTa)O₃-basedpiezoelectric/electrostrictive porcelain composition, a firingtemperature needs to be raised in order to promote crystal grain growth.Therefore, a manufacturing cost respect needs to be improved more. Inthe piezoelectric/electrostrictive device obtained using the(LiNaK)(NbTa)O₃-based piezoelectric/electrostrictive porcelaincomposition or the like, it is difficult to obtain a large displacementas compared with the piezoelectric/electrostrictive device obtainedusing the PZT-based composition containing lead (Pb). It has to be saidthat the PZT-based composition is superior inpiezoelectric/electrostrictive characteristic in the present situations.Therefore, there has been a necessity of developing apiezoelectric/electrostrictive porcelain composition capable ofproviding a device which exhibits the superiorpiezoelectric/electrostrictive characteristic even in a case where anylead (Pb) is not contained.

[Patent Document 1] JP-B-44-17103 [Patent Document 2] JP-B-45-8145[Patent Document 3] JP-A2003-221276

SUMMARY OF THE INVENTION

The present invention has been developed in view of such problemspresent in the conventional technology, and an object thereof is toprovide a piezoelectric/electrostrictive porcelain composition capableof obtaining a piezoelectric/electrostrictive device which is dense andwhich is superior in crystallinity and which exhibits superiorpiezoelectric/electrostrictive characteristics even in a case where thecomposition is fired on lower-temperature conditions as compared withthe conventional technology and to provide a method of manufacturing thecomposition and a piezoelectric/electrostrictive device having superiorpiezoelectric/electrostrictive characteristics.

As a result of intensive investigations to achieve the above-describedobject by the present inventors, it has been found that when compoundscontaining Nb, Ta, and an alkali metal element, respectively are mixedin such a manner as to obtain a non-stoichiometric composition ratio ofNb, Ta, and the alkali metal element, the above-described object can beachieved, and the present invention has been completed.

That is, according to the present invention, there are provided thefollowing piezoelectric/electrostrictive porcelain composition, methodof manufacturing the composition, and piezoelectric/electrostrictivedevice.

According to a first aspect of the present invention, apiezoelectric/electrostrictive porcelain composition is provided,including at least Nb, Ta, and one or more alkali metal elements,wherein a molar ratio of Nb, Ta, and the alkali metal element isrepresented by a non-stoichiometric composition ratio.

According to a second aspect of the present invention, thepiezoelectric/electrostrictive porcelain composition according to thefirst aspect is provided, which is obtained by mixing compoundsincluding metal elements in a composition represented by the followinggeneral formula (1) in such a manner as to satisfy a ratio (molar ratio)of the metal elements in the composition, thereby obtaining a mixture,and then calcining the resultant mixture:A₁(Nb_(x)Ta_(y))O_(3-δ)  (1);wherein A denotes at least one alkali metal element selected from thegroup consisting of Li, Na and K, and 0.7≦(x+y)<1.0.

According to a third aspect of the present invention, thepiezoelectric/electrostrictive porcelain composition according to thesecond aspect is provided, wherein a range of x+y is 0.7≦(x+y)≦0.995 inthe general formula (1).

According to a fourth aspect of the present invention, thepiezoelectric/electrostrictive porcelain composition according to thefirst or second aspects is provided, wherein A in the general formula(1) is represented by the following general formula (2), and ranges of xand y are 0<x<1 and 0<y<1,respectively:Li_(a)Na_(b)K_(c)  (2);wherein 0<a≦0.5,0≦b≦1, and 0≦c≦1.

According to a fifth aspect of the present invention, thepiezoelectric/electrostrictive porcelain composition according to thefirst aspect is provided, which further contains Sb and is obtained bymixing compounds including metal elements in a composition representedby the following general formula (3) in such a manner as to satisfy aratio (molar ratio) of the metal elements in the composition, therebyobtaining a mixture, and then calcining the resultant mixture:A₁(Nb_(x)Ta_(y)Sb_(z))O_(3-δ)  (3);wherein A denotes at least one alkali metal element selected from thegroup consisting of Li, Na and K, and 0.7≦(x+y)<1.0 and 0<z<1.

According to a sixth aspect of the present invention, the method ofmanufacturing a piezoelectric/electrostrictive porcelain composition isprovided, comprising the steps of mixing compounds including metalelements in a composition represented by the following general formula(1) in such a manner as to satisfy a ratio (molar ratio) of the metalelements in the composition, thereby obtaining a mixture; and calciningthe resultant mixture to thereby obtain thepiezoelectric/electrostrictive porcelain composition containing Nb, Ta,and one or more alkali metal elements, a molar ratio of Nb, Ta, and thealkali metal element being represented by a non-stoichiometriccomposition ratio:A₁(Nb_(x)Ta_(y))O_(3-δ)  (1);wherein A denotes at least one alkali metal element selected from thegroup consisting of Li, Na and K, and 0.7≦(x+y)<1.0.

According to a seventh aspect of the present invention, the method ofmanufacturing the piezoelectric/electrostrictive porcelain compositionaccording to the sixth aspect is provided, wherein A in the generalformula (1) is represented by the following general formula (2), andranges of x and y are 0<x<1 and 0<y<1, respectively:Li_(a)Na_(b)K_(c)  (2);Wherein 0<a≦0.5, 0≦b≦1, and 0≦c≦1.

According to an eighth aspect of the present invention, apiezoelectric/electrostrictive device is provided, comprising apiezoelectric/electrostrictive article obtained by firing thepiezoelectric/electrostrictive porcelain composition according to anyone of the first through fifth aspects; and an electrode electricallyconnected to the piezoelectric/electrostrictive article.

According to a ninth aspect of the present invention, thepiezoelectric/electrostrictive device according to the eighth aspect isprovided, wherein the piezoelectric/electrostrictive article and theelectrode have film- like shapes, respectively, and which furthercomprises a substrate made of a ceramic, and thepiezoelectric/electrostrictive article being secured to the substratedirectly or via the electrode.

The piezoelectric/electrostrictive porcelain composition of the presentinvention produces effects that it is possible to obtain thepiezoelectric/electrostrictive device which is dense and superior incrystallinity even in a case where the composition is fired onlower-temperature conditions as compared with the conventionaltechnology and which exhibits superior piezoelectric/electrostrictivecharacteristics.

According to the method of manufacturing thepiezoelectric/electrostrictive porcelain composition of the presentinvention, the piezoelectric/electrostrictive porcelain composition canbe manufactured by firing the composition on lower-temperatureconditions as compared with the conventional technology, so that it ispossible to obtain the piezoelectric/electrostrictive device which isdense and which is superior in crystallinity and which exhibits superiorpiezoelectric/electrostrictive characteristics.

Moreover, the present invention produces an effect that thepiezoelectric/electrostrictive device has superiorpiezoelectric/electrostrictive characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing one embodiment of apiezoelectric/electrostrictive device of the present invention.

FIG. 2 is a sectional view schematically showing another embodiment ofthe piezoelectric/electrostrictive device of the present invention.

FIG. 3 is a sectional view schematically showing still anotherembodiment of the piezoelectric/electrostrictive device of the presentinvention.

FIG. 4 is a sectional view schematically showing a further embodiment ofthe piezoelectric/electrostrictive device of the present invention.

Description of the Reference Numerals Used in the Accompanying Drawings

1 a: secured surface;

1 b: thick portion;

1 c: thin portion;

1: substrate;

2, 3: piezoelectric/electrostrictive article;

4, 5, 6: electrode;

10: piezoelectric/electrostrictive device unit;

12: first piezoelectric/electrostrictive article;

13: second piezoelectric/electrostrictive article;

20: common substrate;- and

51: piezoelectric/electrostrictive device.

DETAILED DESCRIPTION OF THE INVENTION

The best mode for carrying out the present invention will be describedhereinafter, but it should be understood that the present invention isnot limited to the following embodiments, and the present inventionincludes appropriate alterations, modifications and the like added tothe following embodiments based on ordinary knowledge of a personskilled in the art without departing from the scope of the presentinvention.

One embodiment of a piezoelectric/electrostrictive porcelain compositionof the present invention is a piezoelectric/electrostrictive porcelaincomposition containing at least Nb, Ta, and one or more kinds of alkalimetal elements, and a ratio (molar ratio) of Nb, Ta, and the alkalimetal element is represented by a non-stoichiometric composition ratio.Details will be described hereinafter.

The piezoelectric/electrostrictive porcelain composition of the presentembodiment contains at least Nb, Ta, and one or more kinds of alkalimetal elements. It is to be noted that thepiezoelectric/electrostrictive porcelain composition of the presentembodiment is preferably essentially constituted of Nb, Ta, and one ormore kinds of alkali metal elements. Typical examples of the alkalimetal element include Li, Na, and K. The ratio (molar ratio) of Nb, Ta,and the alkali metal element constituting thepiezoelectric/electrostrictive porcelain composition of the presentembodiment is represented by the non-stoichiometric composition ratio.Here, “represented by the non-stoichiometric composition ratio”indicates that a ratio of the respective elements constituting thepiezoelectric/electrostrictive porcelain composition is not representedby a simple integer ratio. To be more specific, the ratio (molar ratio)of a transition metal element group including Nb and Ta constituting a Bsite is not represented by an integer with respect to an alkali metalelement (group) 1 constituting an A site of a perovskite.

Since the ratio (molar ratio) of Nb, Ta, and the alkali metal element isrepresented by the non-stoichiometric composition ratio in this mannerin the piezoelectric/electrostrictive porcelain composition of thepresent embodiment, it is possible to obtain apiezoelectric/electrostrictive device which is dense and superior incrystallinity even in a case where the composition is fired onlower-temperature conditions as compared with a conventional technologyand which exhibits superior piezoelectric/electrostrictivecharacteristics. The following reasons are presumed for such producedeffects.

For example, it is presumed that when the metal elements of the A siteconstituting the perovskite structure are excessive, surface energy dueto defects increases, and a driving force increases. Accordingly, graingrowth is facilitated, and a firing temperature can be lowered. It ispresumed that since automorphism is easily generated in the firedsurface in the conventional piezoelectric/electrostrictive porcelaincomposition represented by a stoichiometric composition ratio,densification of the fired surface is not easily promoted. On the otherhand, it is supposed that in the piezoelectric/electrostrictiveporcelain composition represented by the non-stoichiometric compositionratio, since distortion is included in lattices, the automorphism is noteasily generated in the fired surface, and the densification of thefired surface is promoted.

It is generally known that electric field induced distortion, which isone of characteristics required for a piezoelectric/electrostrictivematerials, is generated when domain rotates in an electric-fielddirection at the time of application of an electric field. It issupposed that the direction of spontaneous polarization is maintainedeven when the electric field is removed in the conventionalpiezoelectric/electrostrictive porcelain composition represented by thestoichiometric composition ratio. On the other hand, it is supposed thata part of the domain returns due to the spontaneous polarizationgenerated by the defects, when the electric field is removed in thepiezoelectric/electrostrictive porcelain composition represented by thenon-stoichiometric composition ratio according to the presentembodiment. This is supposedly because the defects present in thelattices exist symmetrically with the spontaneous polarization of aferroelectric phase, and another spontaneous polarization is generatedin the same direction as that of the spontaneous polarization. That is,the domain rotates reversibly by the application of the electric fieldin the piezoelectric/electrostrictive porcelain composition of thepresent embodiment. Therefore, in the piezoelectric/electrostrictiveporcelain composition of the present embodiment, electric field induceddistortion increases as compared with the conventionalpiezoelectric/electrostrictive porcelain composition in which thedistortion is generated by the only dipole displacement and which isrepresented by the stoichiometric composition ratio.

Additionally, in Japanese Patent No. 3531803, there is disclosed analkali-metal-containing niobium-oxide-based piezoelectric materialcomposition constituted of a solid solution whose composition isrepresented by Li_(x)(K_(1-y)Na_(y))_(1-x)(Nb_(1-z)Ta_(z))O₃. However,this piezoelectric material composition is represented by thestoichiometric composition ratio, and it is not disclosed or suggestedthat the composition is the non-stoichiometric ratio. Effects and thelike are not disclosed or suggested. Therefore, this constitution isapparently different from that of the piezoelectric/electrostrictiveporcelain composition of the present invention which is represented bythe non-stoichiometric composition ratio.

To manufacture the piezoelectric/electrostrictive porcelain compositionof the present embodiment, first, compounds containing Nb, Ta, and thealkali metal element, respectively are mixed to obtain a mixture. Toobtain this mixture, the compounds containing the metal elements,respectively, are preferably mixed in such a manner as to satisfy theratio (molar ratio) of each metal element in the composition representedby the following general formula (1). It is to be noted that there isnot any restriction on types of compounds containing the metal elements,respectively, but an oxide of each metal element, carbonate or the likeis preferably used.A₁(Nb_(x)Ta_(y))O_(3-δ)  (1),wherein A denotes at least one alkali metal element selected from thegroup consisting of Li, Na, and K, and 0.7≦(x+y)<1.0.

When the resultant mixture is calcined, it is possible to obtain thepiezoelectric/electrostrictive porcelain composition of the presentembodiment in which the ratio (molar ratio) of each metal elementconstituting the mixture is represented by the non-stoichiometriccomposition ratio. When a value of “x+y” is less than 0.7, there is sucha tendency that the excessive alkali metal element is not completelydissolved to form another compound, or the element is precipitated ascarbonate or the like to lower insulating resistance. On the other hand,when the value of “x+y” is 1.0 or more, sinterability degrades, theautomorphism is generated, and a densified degree of the fired surfacetends to drop easily. It is to be noted that the value of “x+y” is in arange of preferably 0.7≦(x+y)≦0.995, more preferably 0.90≦(x+y)≦0.99,the most preferably 0.95≦(x+y)≦0.99.

In the piezoelectric/electrostrictive porcelain composition of thepresent embodiment, in the general formula (1), A is represented by thefollowing general formula (2), and ranges of x and y are preferably0<x<1, 0<y<1, more preferably 0.5≦x≦0.95, 0.05≦y≦0.5:Li_(a)Na_(b)K_(c)  (2),wherein 0<a≦0.5, 0≦b≦1, 0≦c≦1.

It is to be noted that transition metal elements other than Nb and Tamay be contained in the B site (site containing Nb and Ta as theconstituting metal elements) in the general formula (1). Examples of thetransition metal element other than Nb and Ta include V, W, Cu, Ni, Co,Fe, Mn, Cr, Ti, Zr, Mo, and Zn.

In addition, it is preferable that the piezoelectric/electrostrictiveporcelain composition of the present embodiment further contains Sb inorder to obtain a piezoelectric/electrostrictive device showing moreexcellent piezoelectric/electrostrictive properties because a largeamount of electrostriction is generated. To obtain apiezoelectric/electrostrictive porcelain composition further containingSb, for example, compounds containing the metal elements are mixedtogether to obtain a mixture in such a manner that the ratio (molarratio) of the metal compounds in the composition shown by the followinggeneral formula (3) is satisfied, and the mixture is calcined to give apiezoelectric/electrostrictive porcelain composition further containingSb of the present embodiment.A₁(Nb_(x)Ta_(y)Sb_(z))O_(3-δ)  (3),wherein A denotes at least one alkali metal element selected from thegroup consisting of Li, Na and K, and 0.7≦(x+y)<1.0 and 0<z<1.

Next, an embodiment of the piezoelectric/electrostrictive device of thepresent invention will be described. The piezoelectric/electrostrictivedevice of the present embodiment is constituted of: apiezoelectric/electrostrictive article obtained by firing any of thepiezoelectric/electrostrictive porcelain compositions according to theembodiment of the present invention; and an electrode electricallyconnected to this piezoelectric/electrostrictive article. That is, thepiezoelectric/electrostrictive device of the present embodiment isconstituted of: a piezoelectric/electrostrictive article obtained byfiring a piezoelectric/electrostrictive porcelain composition whichcontains at least Nb, Ta, and one or more alkali metal elements and inwhich a ratio (molar ratio) of Nb, Ta, and the alkali metal element isrepresented by a non-stoichiometric composition ratio; and an electrodeelectrically connected to this piezoelectric/electrostrictive article.

As described above, according to the embodiment of the presentinvention, in the piezoelectric/electrostrictive porcelain composition,the ratio (molar ratio) of Nb, Ta, and the alkali metal element isrepresented by the non-stoichiometric composition ratio. Therefore, thepiezoelectric/electrostrictive article constituted by firing thispiezoelectric/electrostrictive porcelain composition is dense andsuperior in crystallinity, and has satisfactorypiezoelectric/electrostrictive characteristics. Furthermore, the articleis obtained at a comparatively low firing temperature. Therefore, in thepiezoelectric/electrostrictive device of the present embodiment, anAg—Pd electrode having a melting point lower than that of a Pt electrodecan be positively used. The device is also superior in energy cost andversatility.

In the piezoelectric/electrostrictive device of the present embodiment,an average particle diameter of crystal particles constituting thepiezoelectric/electrostrictive article is in a range of preferably 0.1to 10 μm, more preferably 0.2 to 8.5 μm, especially preferably 0.3 to 7μm. When an average particle diameter is less than 0.1 μm, a domain isnot sufficiently developed in the piezoelectric/electrostrictive articlein some case. Therefore, the piezoelectric/electrostrictivecharacteristics sometimes degrade. On the other hand, when the averageparticle diameter exceeds 10 μm, the domain in thepiezoelectric/electrostrictive article sufficiently develops. On theother hand, the domain does not easily move, and thepiezoelectric/electrostrictive characteristics are reduced in somecases. It is to be noted that the piezoelectric/electrostrictive articleand the electrode constituting the piezoelectric/electrostrictive deviceof the present embodiment can be formed into various shapes. Typicalexamples of the piezoelectric/electrostrictive article include ablock-like shape (so-called bulk article) and a sheet-like shape(film-like shape).

Next, the embodiment of the piezoelectric/electrostrictive device of thepresent invention will be described specifically with reference to thedrawings. FIG. 1 is a sectional view schematically showing oneembodiment of the piezoelectric/electrostrictive device according to thepresent invention. As shown in FIG. 1, in the present embodiment, apiezoelectric/electrostrictive device 51 includes a substrate 1 made ofa ceramic, a film-like piezoelectric/electrostrictive article 2, andfilm-like electrodes 4, 5 electrically connected to thepiezoelectric/electrostrictive article 2. Thepiezoelectric/electrostrictive article 2 is fixed onto the substrate 1via the electrode 4. It is to be noted that thepiezoelectric/electrostrictive article may be directly secured to thesubstrate without disposing any electrode. It is to be noted that in thepresent specification, “secured” indicates a state in which thepiezoelectric/electrostrictive article 2 and the substrate 1 or theelectrode 4 are closely formed integrally with each other without usingany organic or inorganic adhesive.

In the present embodiment, the piezoelectric/electrostrictive article 2of the piezoelectric/electrostrictive device 51 is constituted by firingany of the piezoelectric/electrostrictive porcelain compositionsaccording to the embodiment of the present invention. That is, in thepresent embodiment, the piezoelectric/electrostrictive article 2 of thepiezoelectric/electrostrictive device 51 is constituted by firing thepiezoelectric/electrostrictive porcelain composition which contains atleast Nb, Ta, and one or more alkali metal elements and in which theratio (molar ratio) of Nb, Ta, and the alkali metal element isrepresented by the non-stoichiometric composition ratio.

As described above, in the piezoelectric/electrostrictive porcelaincomposition according to the embodiment of the present invention, theratio (molar ratio) of Nb, Ta, and the alkali metal element isrepresented by the non-stoichiometric composition ratio. Therefore, thepiezoelectric/electrostrictive article 2 formed by firing thispiezoelectric/electrostrictive porcelain composition is dense andsuperior in crystallinity. Therefore, in the present embodiment, thepiezoelectric/electrostrictive device 51 provided with thispiezoelectric/electrostrictive article 2 has satisfactorypiezoelectric/electrostrictive characteristics, and can obtain largedisplacement. Furthermore, the piezoelectric/electrostrictive article 2can be formed at a comparatively low firing temperature. Therefore, theAg—Pd electrode having a melting point lower than that of the Ptelectrode can be positively used, and the device is also superior inenergy cost and versatility.

Moreover, as shown in FIG. 3, the piezoelectric/electrostrictive device51 of the present embodiment may include: a plurality ofpiezoelectric/electrostrictive articles 2, 3; an a plurality ofelectrodes 4, 5, and 6, and the plurality ofpiezoelectric/electrostrictive articles 2, 3 are preferably alternatelysandwiched and layered between the plurality of electrodes 4, 5, and 6.This constitution is a so-called multilayered constitution, and a largeflexural displacement can be preferably obtained at a low voltage.

In the piezoelectric/electrostrictive device 51 (see FIG. 1) of thepresent embodiment, a thickness of the piezoelectric/electrostrictivearticle 2 is in a range of preferably 0.5 to 50 μm, more preferably 0.8to 40 μm, especially preferably 1.0 to 30 μm. In the case where thethickness of the piezoelectric/electrostrictive article 2 is less than0.5 μm, according to the embodiment of the present invention, even thepiezoelectric/electrostrictive article constituted of thepiezoelectric/electrostrictive porcelain composition is insufficientlydensified in some case. On the other hand, when the thickness of thepiezoelectric/electrostrictive article 2 exceeds 50 μm, the compressivestress of the piezoelectric/electrostrictive porcelain composition atthe time of firing increases. In order to prevent the substrate 1 frombeing destroyed, a thicker substrate 1 is required, and it is sometimesdifficult to handle miniaturization of the device. It is to be notedthat as shown in FIG. 3, the thicknesses of thepiezoelectric/electrostrictive articles 2, 3 in a case where thepiezoelectric/electrostrictive device 51 has a so-called multilayeredconstitution refer to those of the piezoelectric/electrostrictivearticles 2, 3, respectively.

In the embodiment of the present invention, the substrate constitutingthe piezoelectric/electrostrictive device is made of a ceramic, butthere is not any special restriction on a type of ceramic. However, withrespect to heat resistance, chemical stability, and insulating property,the ceramic preferably contains at least one selected from the groupconsisting of stabilized zirconium oxide, aluminum oxide, magnesiumoxide, mullite, aluminum nitride, silicon nitride, and glass. Above all,stabilized zirconium oxide is more preferable from a viewpoint that itsmechanical strength is large and its toughness is superior. It is to benoted that “stabilized zirconium oxide” mentioned in the presentspecification refers to zirconium oxide in which phase transition ofcrystals is inhibited by addition of a stabilizer, and includespartially stabilized zirconium oxide in addition to stabilized zirconiumoxide.

Examples of stabilized zirconium oxide include zirconium oxidecontaining as the stabilizer 1 to 30 mol % of calcium oxide, magnesiumoxide, yttrium oxide, scandium oxide, ytterbium oxide, cerium oxide, oroxide of a rare earth metal. Above all, zirconium oxide containingyttrium oxide as the stabilizer is preferable because the mechanicalstrength of a vibrating portion is especially high. In this case,zirconium oxide contains preferably 1.5 to 6 mol %, more preferably 2 to4 mol % of yttrium oxide. Zirconium oxide more preferably contains 0.1to 5 mol % of aluminum oxide. A crystal phase of stabilized zirconiumoxide may be a mixed phase of a cubic system+a monoclinic system, amixed phase of a tetragonal system+the monoclinic system, a mixed phaseof the cubic system+the tetragonal system+the monoclinic system or thelike. However, when a main crystal phase is the tetragonal system, orthe mixed phase of the tetragonal system+the cubic system, the phase ispreferable from viewpoints of strength, toughness, and durability.

It is to be noted that the thickness of the substrate is in a range ofpreferably 1 μm to 1 mm, more preferably 1.5 to 500 μm, especiallypreferably 2 to 200 μm. When the thickness of the substrate is less than1 μm, the mechanical strength of the piezoelectric/electrostrictivedevice sometimes drops. On the other hand, in a case where the thicknessexceeds 1 mm, when a voltage is applied to thepiezoelectric/electrostrictive article. rigidity of the substrateagainst the generated compressive stress increases, and the flexuraldisplacement of the piezoelectric/electrostrictive article is sometimesreduced.

However, as shown in FIG. 2, a shape of the substrate 1 may be providedwith: a thin portion 1 c on whose one surface a secured surface 1 a isformed and which has the above-described thickness; and a thick portion1 b disposed on a portion other than a portion corresponding to thissecured surface 1 a and which has a thickness larger than that of thethin portion 1 c. It is to be noted that the electrode 4 (or thepiezoelectric/electrostrictive article) is disposed in a regionsubstantially corresponding to the secured surface 1 a. When thesubstrate 1 has such shape, a piezoelectric/electrostrictive device canbe constituted which has a sufficiently large flexural displacement andwhose mechanical strength is large. As shown in FIG. 4, a commonsubstrate 20 may be used which is continuously provided with the shapesof the substrates 1 shown in FIG. 2. A plurality ofpiezoelectric/electrostrictive device units 10 each including firstpiezoelectric/electrostrictive article 12, a secondpiezoelectric/electrostrictive article 13, and the electrodes 4, 5, and6 may be disposed on the common substrate 20.

There is not any special restriction on a surface shape (shape of thesurface to which the electrode 4 is secured in FIG. 1) of the substratein the piezoelectric/electrostrictive device according to the embodimentof the present invention. Examples of the surface shape include arectangular shape, a square shape, a triangular shape, an ellipticshape, a circular shape, a round chamfered square shape, a roundchamfered rectangular shape, and a composite shape of a combination ofthese shapes. There is not any special restriction on the whole shape ofthe substrate, and the substrate may have a capsule shape having anappropriate internal space.

In the piezoelectric/electrostrictive device of the present embodiment,the electrode is electrically connected to thepiezoelectric/electrostrictive article, and preferably disposed betweenthe respective piezoelectric/electrostrictive articles. The electrode ispreferably disposed on the piezoelectric/electrostrictive articleincluding a region which substantially contributes to the flexuraldisplacement or the like. For example, as shown in FIG. 3, theelectrodes 4, 5, and 6 are preferably disposed in a region of 80% ormore by area including the vicinity of the center of the surface onwhich the first and second piezoelectric/electrostrictive articles 12and 13 are formed.

In the piezoelectric/electrostrictive device of the present embodiment,examples of a material of the electrode include at least one kind ofmetal selected from the group of Pt, Pd, Rh, Au, Ag, and an alloy ofthem. Above all, platinum or an alloy containing platinum as a maincomponent is preferable in that heat resistance in firing thepiezoelectric/electrostrictive article is high. Since thepiezoelectric/electrostrictive article can be formed at a lower firingtemperature, an Ag—Pd alloy or the like can be preferably used.

In the piezoelectric/electrostrictive device of the present embodiment,the thickness of the electrode is preferably 15 μm or less, morepreferably 5 μm or less. When the thickness exceeds 15 μm, the electrodefunctions as a relaxing layer, and the flexural displacement sometimesdecreases. It is to be noted that the thickness of the electrode may be0.05 μm or more from a viewpoint that the function as a substantialelectrode be exerted.

Next, there will be described one embodiment of a method ofmanufacturing the piezoelectric/electrostrictive porcelain compositionof the present invention. To manufacture thepiezoelectric/electrostrictive porcelain composition of the presentembodiment, first, a compound of each metal element, for example, anoxide or carbonate, is weighed so as to satisfy the ratio (molar ratio)of each metal element in the composition represented by the followinggeneral formula (1), and the compounds are mixed by a mixing method suchas ball milling to obtain a mixed slurry. Typical examples of thecompound of each metal element include Li₂CO₃, C₄H₅O₆Na.H₂O, C₄H₅O₆K,Nb₂O₅, and Ta₂O₅. Subsequently, the resultant mixed slurry can be driedby using a drier or by performing an operation such as filtering toobtain a mixed material. The resultant mixed material can be calcined,and ground if necessary to obtain the piezoelectric/electrostrictiveporcelain composition having a desired particle diameter. It is to benoted that the calcining may be performed at a temperature of 750 to1300° C. The grinding may be performed by a method such as ball milling.A₁(Nb_(x)Ta_(y))O_(3-δ)  (1),wherein A denotes at least one alkali metal element selected from thegroup consisting of Li, Na, and K, and 0.7≦(x+y)<1.0.

An average particle diameter of the piezoelectric/electrostrictiveporcelain composition is preferably 0.07 to 1 μm, more preferably 0.1 to0.7 μm. It is to be noted that the particle diameter may be adjusted byperforming a thermal treatment of powder of thepiezoelectric/electrostrictive porcelain composition at 400 to 750° C.In this case, finer particles are formed integrally with the otherparticles to constitute the powder having a uniform particle diameter,and it is preferably possible to form the piezoelectric/electrostrictivearticle having the uniform particle diameter. Thepiezoelectric/electrostrictive porcelain composition may be prepared byan alkoxide process, a coprecipitation process or the like.

Next, one embodiment of a method of manufacturing thepiezoelectric/electrostrictive device of the present invention will bedescribed in accordance with an example in which shapes of thepiezoelectric/electrostrictive article and the electrode are film-likeshapes, and the device is provided with a substrate made of a ceramic(piezoelectric/electrostrictive film type device). First, a layerconstituted of the piezoelectric/electrostrictive porcelain compositionis formed on the substrate made of the ceramic or on the electrodeformed on the surface of the substrate. Examples of a method of formingthe electrode include ion beam, sputtering, vacuum evaporation, PVD, ionplating, CVD, plating, aerosol deposition, screen printing, spraying,and dipping. Above all, the sputtering method or the screen printingmethod is preferable in respect of a securing property to the substrateand the piezoelectric/electrostrictive article. As to the formedelectrode, an appropriate temperature is selected depending on thematerial or forming method of the electrode, and the electrode can beformed integrally with the substrate and/or thepiezoelectric/electrostrictive article by performing the thermaltreatment at about 500 to 1400° C. This thermal treatment may beperformed every time the electrode is formed, or may be performedtogether with the firing of the layer constituted of thepiezoelectric/electrostrictive porcelain composition. However, afterforming the layer constituted of the piezoelectric/electrostrictiveporcelain composition, the thermal treatment is not performed at atemperature which exceeds the firing temperature of the layerconstituted of the piezoelectric/electrostrictive porcelain composition.

Examples of a method of forming the layer constituted of thepiezoelectric/electrostrictive porcelain composition on the substrateinclude ion beam, sputtering, vacuum evaporation, PVD, ion plating, CVD,plating, sol-gel, aerosol deposition, screen printing, spraying, anddipping. Above all, the screen printing method is preferable because thelayer can be easily continuously formed into a highly precise shape andthickness. It is to be noted that to prepare thepiezoelectric/electrostrictive film type device in which a plurality ofpiezoelectric/electrostrictive articles and electrodes are alternatelysandwiched and layered, the electrode is formed on the layer formed onthe substrate and constituted of the piezoelectric/electrostrictiveporcelain composition by a method similar to the above-described method.It is to be noted that layers constituted of thepiezoelectric/electrostrictive porcelain compositions, and electrodesare alternately and repeatedly formed on the electrode until a desiredmultilayered structure is obtained.

Thereafter, a layer obtained by alternately layering the layersconstituted of the piezoelectric/electrostrictive porcelaincompositions, and the electrodes on the substrate is integrally fired.According to the firing, the film-like piezoelectric/electrostrictivearticle can be secured to the substrate directly or via the film-likeelectrode. It is to be noted that the firing does not have to beintegrally performed, and may be successively performed every time onelayer constituted of the piezoelectric/electrostrictive porcelaincomposition is formed, but it is preferable to integrally fire the layerincluding the electrode from a viewpoint of production efficiency.

In this case, the firing temperature is preferably 800 to 1250° C., morepreferably 900 to 1200° C. When the temperature is less than 800° C.,the substrate or the electrode is incompletely secured to thepiezoelectric/electrostrictive article, or denseness of thepiezoelectric/electrostrictive article sometimes becomes insufficient.On the other hand, when the temperature exceeds 1250° C., thepiezoelectric/electrostrictive characteristics of the resultantpiezoelectric/electrostrictive article sometimes degrade. A maximumtemperature retaining time during the firing is preferably one minute ormore and ten hours or less, more preferably five minutes or more andfour hours or less. When the maximum temperature retaining time is lessthan one minute, the piezoelectric/electrostrictive article isinsufficiently densified, and desired characteristics are not obtainedin some case. When the maximum temperature retaining time exceeds tenhours, there sometimes occurs a disadvantage that thepiezoelectric/electrostrictive characteristics degrade.

Thereafter, a polarization treatment is performed on appropriateconditions. The polarization treatment is preferably performed byheating as in a known method. A heating temperature depends on Curiepoint of piezoelectric/electrostrictive porcelain, and is preferably setat 40 to 200° C.

Moreover, to form the whole piezoelectric/electrostrictive article intoa sheet-like shape, after adding a plasticizer, a dispersant, a solventor the like to the piezoelectric/electrostrictive porcelain compositionto form the composition into a slurry using a general mixing device suchas a ball mill, the slurry is formed into the sheet-like shape by use ofa general sheet forming machine such as a doctor blade.

Furthermore, a conductive film (film containing a conductive material asa main component) constituting the electrode is formed in apredetermined pattern on the surface of thepiezoelectric/electrostrictive article formed into the sheet-like shapeby a technology such as screen printing. Thereafter, the layersconstituted of the piezoelectric/electrostrictive porcelain composition,and the electrodes are alternately layered and attached under pressure,so that a ceramic green layer having a predetermined thickness can beobtained. In this case, a cell structure may be formed by layeringsheets punched by use of a punch or a die. When the resultant ceramicgreen layer is integrally fired, the fired layer can be obtained. It isto be noted that when the cell structure is formed, a cell driving typepiezoelectric/electrostrictive device can be obtained. It is to be notedthat the firing does not have to be integrally performed, but the firingmay be successively performed every time one layer constituted of thepiezoelectric/electrostrictive porcelain composition is formed, but itis preferable to integrally fire the composition including theelectrodes from a viewpoint of production efficiency.

EXAMPLES

The present invention will be specifically described hereinafter basedon examples, but the present invention is not limited to these examples.There will be described methods of measuring various physical values.

[Bulk Density and Apparent Density]: Densities were measured withrespect to a fired article (piezoelectric/electrostrictive article) byArchimedes method.

[Electric Field Induced Distortion]: A distortion gauge was attachedonto the electrode, and an amount of the distortion in a directionvertical to the electric field was measured as the electric fieldinduced distortion (ppm) in a case where a voltage of 4 kV/mm wasapplied.

Example 1

There were weighed Li₂CO₃, C₄H₅O₆Na.H₂O, C₄H₅O₆K, Nb₂O₅, and Ta₂O₅ insuch a manner that a ratio (molar ratio) of each metal element indicateda composition ratio shown in Table 1, and the elements were mixed inalcohol for 16 hours to prepare a mixture. After the resultant mixturewas calcined at 750° C. for five hours, the mixture was ground using aball mill to prepare a piezoelectric/electrostrictive porcelaincomposition. The powder was compacted and formed into a size of adiameter 20 mm×thickness 6 mm under a pressure of 2 t/cm² by use of theresultant piezoelectric/electrostrictive porcelain composition to obtaina green compact. The resultant green compact was stored in an aluminacontainer, and fired at 1000° C. for three hours to obtain a firedarticle (piezoelectric/electrostrictive article). The resultant firedarticle was worked into a size of 12 mm×3 mm×1 mm, opposite surfaces ofthe article were coated with a silver paste to bake an electrode. Thearticle was immersed into silicon oil at 70° C., a direct-currentvoltage of 5 kV/mm was applied between the electrodes for 15 minutes toperform polarization, and a piezoelectric/electrostrictive device(Example 1) was obtained. Various physical values of the resultantpiezoelectric/electrostrictive device are shown in Table 1.

Examples 2 to 5, Comparative Examples 1 to 3

Each piezoelectric/electrostrictive device (Examples 2 to 5, ComparativeExamples 1 to 3) was obtained in the same manner as in the above Example1 except that Li₂CO₃, C₄H₅O₆Na.H₂O, C₄H₅O₆K, Nb₂O₅, and Ta₂O₅ wereweighed in such a manner that a ratio (molar ratio) of each metalelement indicated a composition ratio shown in Table 1. Various physicalvalues of the resultant piezoelectric/electrostrictive device are shownin Table 1.

Examples 6 and 7

Each piezoelectric/electrostrictive device (Examples 6 and 7) wasobtained in the same manner as in the above Example 1 except thatLi₂CO₃, C₄H₅O₆Na.H₂O, C₄H₅O₆K, Nb₂O₅, Sb₂O₃, and Ta₂O₅ were weighed insuch a manner that a ratio (molar ratio) of each metal element indicateda composition ratio shown in Table 1. Various physical values of theresultant piezoelectric/electrostrictive device are shown in Table 1.

TABLE 1 Electric field Bulk Apparent induced density density distortionComposition ratio (g/cm³) (g/cm³) (ppm) Example 1(Li_(0.05)Na_(0.475)K_(0.475))(Nb_(0.90)Ta_(0.08))O_(3−δ) 4.35 4.37 793Example 2 (Li_(0.06)Na_(0.47)K_(0.47))(Nb_(0.90)Ta_(0.08))O_(3−δ) 4.464.47 870 Example 3(Li_(0.07)Na_(0.48)K_(0.45))(Nb_(0.90)Ta_(0.08))O_(3−δ) 4.44 4.45 770Example 4 (Li_(0.07)Na_(0.54)K_(0.39))(Nb_(0.91)Ta_(0.08))O_(3−δ) 4.374.38 560 Example 5(Li_(0.06)Na_(0.58)K_(0.36))(Nb_(0.93)Ta_(0.8))O_(3−δ) 4.42 4.43 630Comp. Ex. 1 (Li_(0.05)Na_(0.475)K_(0.475))(Nb_(0.90)Ta_(0.10))O₃ 4.414.57 504 Comp. Ex. 2 (Li_(0.07)Na_(0.68)K_(0.25))(Nb_(0.90)Ta_(0.10))O₃4.30 4.31 280 Comp. Ex. 3(Li_(0.07)Na_(0.58)K_(0.35))(Nb_(0.92)Ta_(0.08))O₃ 4.30 4.32 370 Example6 (Li_(0.06)Na_(0.575)K_(0.375))(Nb_(0.84)Ta_(0.1)Sb_(0.04))O_(3−δ) 4.434.44 1050 Example 7(Li_(0.06)Na_(0.49)K_(0.45))(Nb_(0.84)Ta_(0.1)Sb_(0.04))O_(3−δ) 4.434.44 900

It is apparent from the results shown in Table 1 that each ofpiezoelectric/electrostrictive devices of Examples 1 to 7 is denser andhas a larger value of electric field induced distortion as compared witheach of the piezoelectric/electrostrictive devices of ComparativeExamples 1 to 3. It is also apparent that each ofpiezoelectric/electrostrictive devices of Examples 6 and 7, each using apiezoelectric/electrostrictive porcelain composition containing Sb inthe B site, has a larger value of electric field induced distortion ascompared with each of the piezoelectric/electrostrictive devices ofExamples 1 to 5, which are manufactured using apiezoelectric/electrostrictive porcelain composition without Sb in the Bsite.

INDUSTRIAL APPLICABILITY

It is possible to obtain a piezoelectric/electrostrictive device whichis dense and superior in crystallinity and which exhibits superiorpiezoelectric/electrostrictive characteristics even in a case where apiezoelectric/electrostrictive porcelain composition of the presentinvention is fired on lower-temperature conditions as compared with aconventional technology. Therefore, the piezoelectric/electrostrictivedevice of the present invention prepared using thispiezoelectric/electrostrictive porcelain composition has superiorpiezoelectric/electrostrictive characteristics, and is suitable for anactuator, a sensor or the like.

1. A piezoelectric/electrostrictive device comprising: apiezoelectric/electrostrictive article obtained by firing apiezoelectric/electrostrictive porcelain composition consisting of Nb,Ta, and one or more alkali metal elements, wherein a molar ratio of Nb,Ta, and the alkali metal element in the firedpiezoelectric/electrorestrictive porcelain composition is represented bya non-stoichiometric composition ratio, and wherein thepiezoelectric/electrostrictive porcelain composition is obtained bymixing compounds including metal elements in a composition representedby the following general formula (1) so as to satisfy a molar ratio ofthe metal elements in the composition, thereby obtaining a mixture, andthen calcining the resultant mixture:A₁(Nb_(x)Ta_(y))O_(3-δ)  (1), wherein A denotes at least one alkalimetal element selected from the group consisting of Li, Na and K, and0.7≦(x+y)≦0.995; and an electrode electrically connected to thepiezoelectric/electrostrictive article.
 2. Thepiezoelectric/electrostrictive device according to claim 1, wherein A inthe general formula (1) is represented by the following general formula(2), and ranges of x and y are 0<x<1and 0<y<1, respectively:Li_(a)Na_(b)K_(c)  (2); wherein 0<a≦0.5,0≦b≦1, and0≦c≦1.
 3. Thepiezoelectric/electrostrictive device according to claim 1 wherein thepiezoelectric/electrostrictive article and the electrode each havefilm-like shapes; wherein the piezoelectric/electrostrictive devicefurther comprises a ceramic substrate; and wherein thepiezoelectric/electrostrictive article is secured to the ceramicsubstrate directly or via the electrode.